1. Field of the Invention
The present invention relates to a tape cassette such as a video tape cassette, and more particularly to a reel lock mechanism for locking a pair of reels in such a tape cassette when it is in an inoperative condition.
2. Description of the Related Art
FIGS. 6 and 7 show conventional video tape cassettes, e.g., 8 mm video tape cassettes, having different internal structures. Commonly in these video tape cassettes, a magnetic tape 1 is wound around a pair of reels 2 and 3 rotatably mounted in a cassette housing 4. The stacks of the magnetic tape 1 around the reels 2 and 3 are partially drawn and stretched between a pair of tape guides 5 for guiding the magnetic tape 1 passing along a front opening 6 of the cassette housing 4. A front lid 8 is vertically pivotably supported to a pair of support pins 7 formed on opposite side walls 4a of the cassette housing 4 at a front end portion thereof, so as to normally close the front opening 6 and cover the span of the magnetic tape 1 along the front opening 6.
A reel lock mechanism 9 is provided in a substantially triangular space defined between the reels 2 and 3 on the side of a rear wall 4b of the cassette housing 4. The reel lock mechanism 9 serves to lock rotation of the reels 2 and 3 in the opposite directions of slacking of the magnetic tape 1 as shown by arrows a and a' when the video tape cassette is ejected from a video tape recorder to become inoperative.
The details of the reel lock mechanisms 9 in the video tape cassettes shown in FIGS. 6 and 7 will be described with reference to FIGS. 8A and 8B, respectively.
First in the reel lock mechanism 9 shown in FIG. 8A, a slider 11 is engaged between a pair of ribs 10 integrally formed with a bottom plate 4c and the rear wall 4b of the cassette housing 4. The slider 11 is slidable in a frontward direction as depicted by an arrow b and a rearward direction as depicted by an arrow c. A compression coil spring 12 is interposed under compression between the slider 11 and the rear wall 4b to normally bias the slider 11 in the frontward direction b. A pair of elastic lock pawls 13 and 14 having a substantially V-shaped configuration are formed on the front surface of the slider 11. In the inoperative condition of the video tape cassette, the lock pawls 13 and 14 are engaged with outer circumferential toothed portions 15 and 16 of lower flanges 2a and 3a of the reels 2 and 3, respectively, thereby locking the rotation of the reels 2 and 3 in the directions a and a' to establish a reel lock condition.
On the other hand, in the reel lock mechanism 9 shown in FIG. 8B, a pair of lock pawls 17 and 18 each having a substantially V-shaped configuration are pivotably mounted on a pair of vertical support shafts 19 and 20 formed on the bottom plate 4c of the cassette housing 4, respectively. That is, the lock pawls 17 and 18 are rotatably about the vertical support shafts 19 and 20 in the opposite directions as depicted by arrows d and e and in the opposite directions as depicted by arrows d' and e', respectively. A pair of torsion springs 21 and 22 are mounted on the vertical support shafts 19 and 20 at the upper end portions thereof, respectively. The torsion spring 21 is engaged at one end thereof with the lock pawl 17, and the other end of the torsion spring 21 is engaged with the rear wall 4b of the cassette housing 4, thereby normally biasing the lock pawl 17 in the rotational direction d and engaging a catching end of the lock pawl 17 with the toothed portion 15 of the reel 2. Similarly, the torsion spring 22 is engaged at one end thereof with the lock pawl 18, and the other end of the torsion spring 22 is engaged with the rear wall 4b, thereby normally biasing the lock pawl 18 in the rotational direction d' and engaging a catching end of the lock pawl 18 with the toothed portion 16 of the reel 3. Accordingly, the rotation of the reels 2 and 3 in the directions a and a' is locked by the reel lock mechanism 9 to establish a reel lock condition. Further, a pair of ribs 23 serving as guides are formed on the bottom plate 4c, and an unlocking slider 24 is engaged between the ribs 23 so as to be slidable in the frontward direction b and the rearward direction c. The slider 24 is normally biased by a compression coil spring 25 in the frontward direction b. The other ends of the lock pawls 17 and 18 are in contact with the rear surface of the slider 24.
When the video tape cassette is loaded into the video tape recorder to establish an operative condition, the reel lock mechanism 9 shown in FIG. 8A is operated in such a manner that the slider 11 is retracted in the direction c against the compression coil spring 12 to thereby disengage the lock pawls 13 and 14 from the toothed portions 15 and 16, respectively, thus releasing the reel lock condition.
On the other hand, the reel lock mechanism 9 shown in FIG. 8B is operated in such a manner that the slider 24 is retracted in the direction c against the compression coil spring 25 to thereby rotate the lock pawls 17 and 18 against the torsion springs 21 and 22 in the directions e and e', respectively, and resultantly disengage the lock pawls 17 and 18 from the toothed portions 15 and 16, thus releasing the reel lock condition.
However, in the reel lock mechanism 9 shown in FIG. 8A, when the lock pawl 13 only is urged in the direction c by the toothed portion 15 of the reel 2 because of vibration, shock, etc. during transportation of the video tape cassette, there is a possibility that the other lock pawl 14 will disengage from the toothed portion 16 of the other reel 3 to cause undesirable rotation of the reel 3 in the direction b. As a result, the magnetic tape 1 as shown in FIG. 6 is prone to slack in the direction a'.
In the reel lock mechanism 9 shown in FIG. 8B, if the biasing forces of the torsion springs 21 and 22 are set to be large, so as to exhibit a sufficient reel locking performance, the reels 2 and 3 receive large sliding forces in the directions as depicted by arrows F and F' in FIG. 7 at the time the lock pawls 17 and 18 are brought into engagement with the toothed portions 15 and 16 by the torsion springs 21 and 22. As a result, the magnetic tape 1 as shown in FIG. 7 is prone to slack in the directions a and a'. In contrast therewith, if the biasing forces of the torsion springs 21 and 22 are set to be small, a sufficient reel locking performance cannot be exhibited.